Methods for the production of glycols, i.e. terminally substituted aliphatic diols, are known to the art. Among desired glycols are those having four or more carbon atoms such as 1,6-hexanediol and especially, 1,4-butanediol.
1,4-butanediol and 1,6-hexanediol are useful as monomers in a number of polymers including, thermoplastics such as the polyester thermoplastics and polyether thermoplastics. Particular such thermoplastics are poly(1,4-butylene terephthalate) resin block copolymers containing blocks of poly(butyl ether) and aliphatic polyesters such as poly(hexylene adipate).
Particularly, 1,4-butanediol may be produced in a number of processes. The most commonly used process involves reacting acetylene and formaldehyde by the REPPE reaction to give but-2-yne-1,4-diol which is hydrogenated to form 1,4-butanediol. Another method, reacts allyl alcohol, produced from propylene, with i-butylene to form allyl t-butyl ether which is hydroformylated over a rhodium complex catalyst to give 4-t-butoxybutyraldehyde. This compound is then hydrogenated and cleaved under mild conditions over an acid catalyst to give 1,4-butanediol.
More pertinent to the present invention, there have also been a number of proposals to produce 1,4-butanediol in a single hydrogenation step from a diester of maleic acid or in a two step process converting maleic anhydride first to gamma-butyrolactone and subsequently in a second reaction step to 1,4-butanediol. Several references have dealt with the conversion of gamma-butyrolactone to 1,4-butanediol. The majority of such references recommend the liquid phase for carrying out the reaction. However, it is known to conduct the reaction in the vapor phase as well.
WO No. 82/03854, Bradley, et al., discloses the hydrogenolysis of gamma-butyrolactone in the vapor phase over a copper oxide and zinc oxide catalyst. Reactor productivity is generally low.
British Pat. No. 1,230,276 discloses the hydrogenation of gamma-butyrolactone using a copper oxide-chromium oxide catalyst. The hydrogenation is carried out in the liquid phase. Batch reactions are exemplified having very high total reactor pressures. Reactant and product partial pressures in the reactors are well above the respective dew points.
British Pat. No. 1,314,126 discloses the hydrogenation of gamma-butyrolactone in the liquid phase over a nickel-cobalt-thorium oxide catalyst. Batch reactions are exemplified having high total pressures and component partial pressures well above respective component dew points.
British Pat. No. 1,344,557 discloses the hydrogenation of gamma-butyrolactone in the liquid phase over a copper oxide-chromium oxide catalyst. A vapor phase or vapor containing mixed phase is indicated as suitable in some instances. A continuous flow tubular reactor is exemplified using high total reactor pressures.
British Pat. No. 1,512,751 discloses the hydrogenation of gamma-butyrolactone to 1,4-butane diol in the liquid phase over a copper oxide-chromium oxide catalyst. Batch reactions are exemplified with high total reactor pressures and, where determinable, reactant and product partial pressures well above the respective dew points.
U.S. Pat. No. 4,301,077 discloses the hydrogenation to 1,4-butanediol of gamma-butyrolactone over a Ru-Ni-Co-Zn catalyst. As taught, the reaction may be conducted in the liquid or gas phase or in a mixed liquid-gas phase. Exemplified are continuous flow liquid phase reactions at high total reactor pressures and relatively low reactor productivities.
U.S. Pat. No. 4,048,196 discloses the production of 1,4-butanediol by the liquid phase hydrogenation of gamma-butyrolactone over a copper oxide-zinc oxide catalyst. Exemplified is a continuous flow tubular reactor operating at high total reactor pressures and high reactant and product partial pressures.
The process of the above references are convenient to produce laboratory quantities of 1,4-butanediol. However, on scale-up, it is discovered that generally low reactor productivities necessitate large reactors to produce commercial quantities. Such large reactors are impractical using the high pressures of the prior art references.
Therefore, it is an object of the present invention to produce glycols from lactones, and in particular, 1,4-butanediol from gamma-butyrolactone.
It is another object of the present invention to increase reactor productivity in the hydrogenation of lactones to diols.
It is another object of the present invention to lower overall reactor pressure during such hydrogenation while increasing reactor productivity.